The invention relates to instantaneous gas water heaters or bath heaters of the type without a permanent pilot light, operating without a battery and operating without connection to the electric mains. The invention including a small hydraulic turbo-alternator which is set in rotation by the water flowing through the water heater for the whole time during which hot water is drawn, which, in connection with a small electrovalve driving a differential membrane gas valve, provides automatically, whenever a tap is opened for drawing hot water, the following known and successive operations: lighting of the gas at the pilot light, checking the existence of a flame at the head of this pilot light, and then controlling the arrival of the gas at the burner.
Such an apparatus was described in the French Pat. No. 1 215 731 filed on the Nov. 7, 1958.
However, for several reasons it was not possible to make a commercially practical embodiment of that prior device. For example no solution was available up to the present time which was both sufficiently economical and sufficiently reliable for controlling the electrovalve from the current produced by the turbo-alternator, so as to provide thermostatic regulation of the water drawn off by making the gas flow rate automatically dependent on the temperature of the water drawn off.